Vessel for production and/or loading/unloading and transport of hydrocarbons from offshore fields, and/or for carrying out well operations

ABSTRACT

A vessel for use in offshore production or transport of hydrocarbons, and/or for loading/unloading of hydrocarbons, and/or for carrying out well operations. The vessel at its forward end is equipped with a submerged receiving space for receiving a bottom-anchored underwater buoy. A service shaft extends between the receiving space and the deck of the vessel. At the stern of the vessel, a coupling head is provided along with equipment for the connection of a hose for loading and unloading of oil.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a vessel for use in production or transport ofhydrocarbons from offshore fields. Further, the invention relates to amethod for loading of oil from a loading hose which is connected to anunderwater buoy and which, for connection, is pulled up onto the deck ofa vessel and connected to a loading manifold on the deck.

2. Brief Description of the Prior Art

There are previously known ships which are used for transport of oilfrom offshore loading buoys to e.g. a land-based oil terminal (shuttletankers). These load oil via a loading hose from the loading buoy, thehose being pulled over the bow of the ship and connected to a couplinghead on the ship.

Recently, there have also become known shuttle tankers which arearranged to connect themselves to underwater loading buoys whichsimultaneously keep the ship anchored. There has also been proposed sucha buoy which comprises a swivel unit having several pipe courses andwhich is adapted for production purposes.

There are also known storage vessels which are fixedly anchored, and areconnected to a production platform via a hose or pipeline. Unloadingtakes place via a loading system which is placed at the stern of theship where it is connected to a loading hose which is pulled over thebow of a shuttle tanker.

It is an object of the invention to provide a vessel which by simplemeans is able to change between operating as

a) a production vessel which is connected to an underwater buoy by meansof a swivel,

b) a shuttle tanker which connects itself to a submerged loading buoy,

c) a storage vessel which is permanently connected to an underwaterbuoy, and which simultaneously has unloading equipment at the stern ofthe vessel for unloading oil, and

d) a shuttle tanker which connects itself to loading hoses pulled overthe deck of the tanker.

SUMMARY OF THE INVENTION

The above-mentioned object is achieved with a vessel of theintroductorily stated type which, according to the invention, ischaracterized in that the vessel near to its forward end comprises asubmerged receiving space for receiving an underwater buoy, and aservice shaft extending between the receiving space and the deck of thevessel, and that the vessel further, at its stern on the deck, comprisesa coupling head and equipment for connection of a hose forloading/unloading of oil.

An advantageous embodiment of the vessel according to the invention ischaracterized in that its stern in plan view has a pointed, roundedshape (bow shape). By means of this embodiment there is achieved thatthe forces acting on the stern because of waves and wind, are reduced asmuch as possible. An additional advantage of this hull shape is achievedif a load transfer between two vessels is to be undertaken. If thevessels during the load transfer should get in contact with each other,possible damages will be substantially reduced compared to if the vesselhas a traditional, transverse stern which the rearwardly located vesselruns into.

The placing of loading/unloading equipment at the stern of the vesselhas an additional advantage if the vessel operates as a traditionalshuttle tanker and is to load from a submerged hose, for example inconnection with a buoy of the UKOLS type. In such situations the vesselwill be lying with the bow against the wind and connect itself to theloading hose with the stern to leeward.

With traditional connection, with loading equipment arranged on the bow,and with the bow placed in position against the wind when connecting,that which limits the loading operation, when the ship is able toconnect itself to the loading hose and remain connected, will be thesecurity of the crew moving on the deck and carrying out the connection.With waves having a significant wave height one of around 5.5 meters istoday prevented from carrying out loading.

By carrying out loading at the lee end of the vessel, one can effectconnection and continue loading at wave heights up to 8 m significantwave height.

Thus, according to the invention, there is also provided a method of theintroductorily stated type which, according to the invention, ischaracterized in that the loading manifold is placed at the stern of thevessel, that the ship prior to the connection is positioned with the bowtowards the wind at the windward side of the buoy, and that the vesselis moved form this position so that its stern gets into position to beconnected to the loading hose.

It is an additional advantage of the invention that the wheelhouse ofthe vessel and its engine room can be placed quite at the bow portion ofthe vessel. The service shaft up from the receiving space of the vesselthen will be placed just behind the wheelhouse, and thus will be underthe lee of the wheelhouse. With such a configuration there issimultaneously obtained a large deck area from the rearward part of thewheelhouse and backwards to the rearward deck area. When the vessel isto be used as a production vessel, this area will be able to be used fornecessary process equipment and equipment for well control.

Since the vessel is to be able to change between different fields ofactivity, it is preferable that the whole process installation isdivided into smaller portable modules.

The invention will be further described below with reference to thedrawings, wherein

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a side view of a vessel according to the invention;

FIG. 2 shows a side view of the vessel wherein oil is produced form amanifold at the sea bed, at the same time as maintenance is effected ofan oil well which is connected to the manifold;

FIG. 3 shows a side view of the vessel when loading from a loading hosewhich is connected to an underwater buoy;

FIG. 4 shows a side view of the rearward part of the vessel;

FIG. 5 shows a plan view of the stern of the vessel;

FIG. 6 shows a plan view of the poop deck of the vessel; and

FIG. 7 shows a side view of the forward part of the vessel.

DETAILED DESCRIPTION OF THE INVENTION

A vessel 1 according to the invention is schematically shown in sideview in FIG. 1. As shown, at the forward end of the vessel there isarranged a submerged, downwardly open receiving space 2 for receiving anunderwater buoy 3, and a service shaft 4 extends between the receivingspace 2 and the deck 5 of the vessel. The arrangement is designed suchthat a submerged buoy for loading/unloading of hydrocarbons can bepulled up and secured in the receiving space, as further shown anddescribed in the Norwegian patent applications Nos. 923814-923816, andfurther such that a buoy which is arranged to cooperate with a swivelunit arranged at the lower end of the shaft, can be pulled up andsecured, for use of the vessel as a production vessel, as further shownand described in the Norwegian patent applications Nos. 922043-922045.Reference is here made to said applications, for a further descriptionof the topical embodiments.

Since the forward part of the vessel essentially is constructed inaccordance with prior art, only an overview of the most essential onesof the parts and elements shown in the Figure will be given here.

As appears, the wheelhouse 6 of the vessel is placed near to the bow 7of the vessel, and further the engine room 8 with the diesel-electricmain machinery thereof is placed below the wheelhouse. The service shaft4, which extend between the buoy 3 and the deck 5 of the vessel, isplaced just behind the wheelhouse, so that crew which is to go down intothe shaft, will be in lee behind the wheelhouse.

Above the buoy there is shown to be arranged a loading manifold/swivel 9for connection to the buoy 3, and also a connecting pipe with an oilpipe valve 10. Loading manifold/swivel 9 is movable such that it can betaken away from the shaft and clear the shaft when the swivel is not inuse. Further, there are shown monitoring means 11, e.g. TV cameras, ashutter 12 for shutting-off the shaft 4 over the receiving space, and aguide means 13 for use in connection with pulling-up of the buoy. On thedeck there is further shown to be arranged a pulling winch 14, a storageunit 15 and a service crane 16 for use in connection with i.a.maintenance. In the bow of the vessel there is arranged a pair of bowpropellers 17.

At the rearward end of the vessel there is i.a. arranged equipment forloading/unloading of oil by means of equipment which is also essentiallybased on prior art. On the previously known, conventional vessels suchequipment is arranged in the bow portion thereof, whereas--on thepresent vessel--it is arranged at the stern of the vessel. This impliessubstantial operational advantages, as also mentioned in theintroduction. and in combination with the aforementioned receiving spaceand the appurtenant equipment at the forward end of the vessel there areobtained substantial advantages with respect to flexibility andversatile use of the vessel.

From the main elements arranged on the deck at the stern of the vessel,FIG. 1 shows a coupling head in the form of a loading manifold 20 with aswivel, a hose windless 21, a hose handling winch 22 and TV monitoringequipment 23. Further, there are shown a control room 24 and ahydraulics room 25. Additional elements forming part of theloading/unloading equipment at the stern are to be mentioned inconnection with FIGS. 4-6.

Process equipment for the processing of oil is arranged on the deckbetween the forward and the rearward part of the vessel. This equipmentis shown in the form of a number of portable modules 26. Between theforward and the rearward part, the vessel contains a number of cargocompartments or tanks 28. In the rearward area there is also shown to bearranged a flare boom 27. The main propeller 29 of the vessel is shownto be connected to an electric driving motor 30.

Some of the different combination possibilities as regards applicationsof the vessel according to the invention, are to be mentioned below.

FIG. 2 shows an application wherein produced oil from an oil well issupplied to the vessel from a manifold 35 at the sea bed 36, at the sametime as maintenance is effected of an oil well 37 which is connected tothe manifold 35. In this case necessary equipment for carrying out themaintenance operations is arranged at the stern of the vessel, where theequipment by suitable means 38 is guided down to the well head via e.g.a wire or pipeline 39. Then manifold 35 at the sea bed is connected tothe buoy 3 via flexible risers 40. As described in the aforementionedpatent applications, the buoy 3 is bottom-anchored by means of asuitable anchor system (not shown in the drawings), so that the buoyalso constitutes an anchoring buoy for the vessel.

This application of the vessel is particularly advantageous when anumber of wells 37 are arranged in a circle at the sea bed around themanifold 35, and the distance between the manifold and the wells isessentially equal to the length of the vessel. The vessel then can bepermanently connected to the manifold 35 via the buoy 3, and produce oilfrom the manifold, at the same time as maintenance of the differentwells can be carried out from the stern of the vessel, the vessel beingable to be turned about the buoy as required, so that its stern can beplaced over the well of interest. In this manner maintenance/control ofbottom-mounted multiphase equipment and process equipment can be carriedout during production, which is very advantageous, especially in deepwaters.

The vessel of course also can be used only for production from an oilwell via the buoy in the receiving space, or only for well maintenancevia the rearward end of the vessel, without combining these operations.Possible, well maintenance can be carried out via the service shaft 4and the receiving space 2, with dynamic positioning of the vessel.

FIG. 3 shows another application wherein oil is loaded from a loadinghose 41 which is connected to an underwater buoy 42, the hose beingpulled up onto the deck of the vessel and connected to the loadingmanifold 20. Such buoy loading advantageously is carried out inaccordance with the method mentioned in the introduction.

Oil may also be loaded via a transfer conduit or a riser which iscoupled to a loading buoy in the receiving space, where the buoy is ofthe type which, for example, is mentioned in the aforementionedNorwegian patent application No. 923815.

Oil loading also may take place via the stern of the vessel inconnection with other types of loading devices, e.g. spar-buoy buoys(spar type loading), buoys floating on the surface of the water, orarticulated (buoy) columns.

The vessel also may be used for carrying out well tests, both via theforward service shaft and from the stern of the vessel, in both caseswith dynamic positioning.

The vessel also may constitute a storage for oil, and according torequirement unload the oil over to e.g. a shuttle tanker by means of ahose connection between the stern of the vessel and the shuttle tanker.

The different parts and elements arranged on the vessel according to theinvention are more clearly shown in the enlarged views in FIGS. 4-7.

In addition to the elements mentioned above, in the side view of FIG. 4and in the plan view of FIG. 5 there are shown a guide roller 45, ahydraulic pump station 46, a storage unit 47, a service crane 48, apulling winch 49, a fairlead 50, bunker line drums 51 and a chainstopper 52.

FIG. 6 shows the poop deck of the vessel where the loading manifold 20and the hose handling winch 22 are arranged. Further, the Figure shows amanifold control console 53 and a storage unit 54.

In FIG. 7, which shows the forward part of the vessel, the buoy 3 isomitted. In addition to the parts and elements mentioned above there issuggested, in connection with the wheelhouse 6, a steering console 55arranged ont he navigating bridge, and there are also suggested ahydraulic pump station 56 and starter cabinets 57. In other respectsreference is made to the aforementioned patent applications, for afurther description of the constructive embodiments of the buoy, and theequipment arranged in connection with the receiving space and theservice shaft.

We claim:
 1. A vessel capable of alternating between operation as aproduction ship for hydrocarbon production, as a storage ship onoffshore fields, and as a shuttle tanker, the vessel comprising incombination:(a) a submerged, downwardly-open receiving space at a bow ofthe vessel for receiving a bottom-anchored underwater buoy for transferof hydrocarbons, (b) a service shaft extending between the receivingspace and a deck of the vessel, (c) a swivel unit arranged at a lowerend of the service shaft, for connection of the buoy to a pipe system onthe vessel, the swivel unit being movably arranged to be taken away fromthe shaft and clear the shaft when the swivel is not in use, (d) acoupling head and equipment for connection of a hose forloading/unloading of oil, the coupling head being disposed at a stern ofthe vessel, and the equipment being disposed at the stern for executionof operations on sea bed installations or wells at the same time as thevessel is anchored to the underwater buoy.
 2. A vessel according toclaim 1, wherein the stern in plan view has a pointed, rounded shape. 3.A vessel according to claim 2, having a wheelhouse placed near to theforward end of the vessel, and wherein the receiving space for the buoyand the service shaft up from the receiving space are placed just behindthe wheelhouse, so that crew going down into the shaft will be in leebehind the wheelhouse.
 4. A vessel according to claim 2, whereinequipment for execution of operations on sea bed installations or wellsis also arranged in connection with the service shaft.
 5. A vesselaccording to claim 1, having a wheelhouse placed near to the bow of thevessel, and wherein the receiving space for the buoy and the serviceshaft up from the receiving space are placed just behind the wheelhouse,so that crew going down into the shaft will be in lee behind thewheelhouse.
 6. A vessel according to claim 1, wherein the equipment forexecution of operations on sea bed installations or wells is alsoarranged in connection with the service shaft.
 7. A method of loadingoil from a loading hose connected to an underwater buoy, wherein thehose is connected to a vessel having a bow, a stern, a deck, a submergedreceiving space disposed at the bow for receiving an underwater buoy, aservice shaft extending between the receiving space and the deck, and acoupling head and equipment disposed on the deck at the stern forconnection of the loading hose, the method comprising the steps of:a.positioning the vessel with the bow towards the wind at the windwardside of the buoy, b. moving the vessel from position (a) so that thestern gets into position to be connected to the loading hose, c. pullingthe loading hose up onto the deck, and d. connecting the loading hose toa manifold of the coupling head at the stern.
 8. A method of loading oilfrom a loading hose connected to an underwater buoy, wherein the hose isconnected to a vessel capable of alternating between operation as aproduction ship for hydrocarbon production, as a storage ship onoffshore fields, and as a shuttle tanker, the vessel including asubmerged, downwardly-open receiving space at a bow of the vessel forreceiving a bottom-anchored underwater buoy for transfer ofhydrocarbons, a service shaft extending between the receiving space anda deck of the vessel, a swivel unit arranged at a lower end of theservice shaft, for connection of the buoy to a pipe system on thevessel, the swivel unit being movably arranged, to be taken away fromthe shaft and clear the shaft when the swivel is not in use, a couplinghead and equipment for connection of a hose for loading/unloading ofoil, the coupling head being disposed at a stern of the vessel, and theequipment being disposed at the stern for execution of operations on seabed installations or wells at the same time as the vessel is anchored tothe underwater buoy; the method comprising the steps of:(a) positioningthe vessel with the bow towards the wind at the windward side of thebuoy, (b) moving the vessel from position (a) so that the stern getsinto position to be connected to the loading hose, (c) pulling theloading hose up onto the deck, and (d) connecting the loading hose to amanifold of the coupling head at the stern.